The overall objective of this project is to investigate the efferent and higher order afferent projections from individual vestibular receptors in the adjult pigeon. More specifically, (1) to demonstrate vestibular efferent projections from individual cristae and maculae in the adjult animal using horseradish peroxidase (HRP) reacted by the highly sensitive tetramethylbenzidine blue reaction process, (2) to demonstrate higher order afferent projections from individual vestibular receptors using transsynaptically transported 3H-labeled proline-fucose, (3) to determine if the HRP-labeled efferent neurons in the reticular formation are catecholaminergic with fluorescence techniques, and (4) to investigate whether HRP-labeled reticular afferent neurons project to both labyrinths spontaneously. To do this, we will (1) deliver discrete amounts of neural tracer equally to the entire receptor enuroepithelial surface by injecting and confining HRP or proline-fucose to the membranous endolymphatic space, (2) isolate individual receptors by selective axotomy permitting intraaxonal tracer transport from only the isolated receptor neuroepithelium, and (3) use transcardiac catheterization to obtain ultrastructural quality fixation of the brain, labyrinths, and upper spinal cord. We will construct accurate 2-plane (coronal, sagittal) neuronal maps (with cell counts, cell dimensions, and fiber tract densities) of labeled efferent and higher order afferent projections within the brain and spinalcord, and synthesize our findings to define durther the anatomical organization of individual vestibular receptor projections. The expected results will provide a sound basis for future electrophysiological studies, and indirectly contribute to a better understanding of clinical disorders such as Meniere's diseases.